baxi has mind of its own

[glynbt]

I have a Baxi maxflow WM.

The heating has been firing up when the boiler is supposed to be off, as per the timer, and the heating still fires up when switched over to hot water only. It has also been turning off when it is supposed to be on. The 'fault finding' steps don't seem to deal with this problem.

I hope it is simply a PCB (?ignition), but any advice welcomed

 

[gstens baxi]

If the boiler is fitted in a cold location it could be the frost stat bringing it on.

 

[gazthepottertonengineer]

or it could be the 3 port valve this boiler has the very common honeywell type with actuator built in that sometimes sticks

 

[glynbt]

Thanks for these.

It's not in a cold place, so i think thats unlikely. Are there simple ways of perhaps releasing the valve, or does this need replacing?
Ultimately it sounds like it needs looking by an engineer eh?